1. Field of the Invention
This invention relates to terminal leads for electronic components, and in particular it relates to a terminal lead having an improved clip for attachment to the substrate onto which a miniature solid state electronic component is deposited.
2. Description of the Prior Art
The use of miniature solid state electronic components has grown dramatically in recent years. One such type of component enjoying particular popularity is the type in which a solid state component is deposited on a ceramic substrate, with metallized areas deposited on the substrate as electrical contacts for the component. Terminal leads are soldered to the contact areas, and the substrate is finally encased in a molded plastic housing. Such a construction has become increasingly popular, for example, for miniature potentiometers employing a deposited carbon or cermet resistive element.
One persistent problem with this type of construction relates to the connection between the terminal leads and the metallized areas on the substrate. Prior to soldering, a mechanical connection is obtained by engaging the substrate in a clip-like member formed in the end of the lead. This clip-like member or "terminal clip" is typically formed by a pair of prongs, one of which is bent upwardly, and the other of which is usually unbent, but may be bent downwardly. The substrate is thus grasped between the two prongs. This arrangement has two major shortcomings, both resulting from the limited length of the terminal lead which is encased in the housing.
Firstly, because there is such a relatively short length of lead extending into the housing to the solder joint, any bending of the lead subsequent to the encasement of the substrate will cause a major portion of the resulting stress to be applied to the solder joint, thereby weakening the joint and making repeated lead bending inadvisable if the integrity of the joint is to be assured.
Secondly, since there is only a limited contact area between the terminal lead and the housing material, and since a substantial portion of this contact area is between the edge of the substrate and the surface of this housing, adequate sealing of the substrate from the outside environment cannot easily be assured, especially when thermoplastics are used for the housing material. Thus, at present, thermosets, which take a relatively long time to mold, are typically used for the housings.
In view of the foregoing, it can be appreciated that there has been a long-felt need for a terminal clip structure which provides stress relief for the solder joint, while also providing an improved sealing capability when the substrate is encased in its associated housing.